generator differential protection relay

 

generator differential protection relay mainly used in the Small and medium sized differential protection device , water tribute generator used the 9698A differential protection, which has the function of differential current instantaneously trip protection,Proportional differential protection（with Two harmonic brake、CT line-break locking）、CT line-break alarm,Non electricity protection、Transverse differential protection,also the multiple communication interface of the 485 communication, internet communication and Optical fiber communication.
Scope of application
Mainly used in the Small and medium sized differential protection device 
water tribute generator used the 9698A differential protection
steam turbine generator used the 9698B differential protection.
 
Protection function
differential current instantaneously trip protection
Proportional differential protection（with Two harmonic brake、CT line-break blocking）
CT line-break alarm
Non electricity protection
Hydraulic accidents－Tripping operation（Fire Power Generator： Hydraulic accidents－Tripping operation）
   exciter accident－Tripping operation；
     Electrical accident－Tripping operation；
 Transverse differential protection(Apply to the generator protection whose every phase consists of parallel windings）；
 
Measurement and control function
     High side current：IA、IB、IC；
     Low side current：Ia、Ib、Ic；
     Differential current：DIa、DIb、DIc；
 
Auxiliary function
Fault recording; 
Communication mode
     485communication；
    Ethernet communication;
 Optical fiber communication;
 
Protective action principle 
①  Pilot differential current instantaneously trip protection   
  Which in essence reflect the protection act quickly the two side current of the generator ,when the  interior generator occurs serious fault or the external two side of the transformer occurs short circuit ,then act and trip quickly.
Protective action criterion：Icd >Isd 
     among：Icd is the actual differential current of the same phase CT of the two side,Isd is the differential instantaneous fixed current value.    
 Three of them meet the requirement  that Icd >Isd  then the differential will work to trip all the switch of the main transformer.
     The differential current in the actual function=  Id + Iww 
②  Ratio differential protection（with the function of ＣＴ line-break  ）
     which used the split phase type that is any one of the Ａ、Ｂ、Ｃ phase will act and output the value.the following will judge it by the example of one phase     
When all the following inequation come into existence, then the ratio differential protection will work for protection
generator differential protection relay.png
among：Ｉd、Ｉw Respectively as the end and the tail current of the device.
     Ｉsd is the differential current instantaneous fixed value.
Ｉcdqd is the differential protection threshold fixed value;
     Ｉzd is the immobilize current;
     Ｉe is the rated current of generator
     Differential protection of ratio immobilize： 
    Icd＞Icdqd    Icd＞1*Izd   （you can choose “or ‘ for them’）
     among：Icd is the differential current，Izd is the immobilized current ，K1 is the Ratio immobilized coefficient.Icdqd is the differential current threshold fixed value 
     Icd＝| Id＋Iw |    Izd＝| Id一Iw |／2
     Simple calculation in debugging：
    If the proportional differential action，then  Icd＝| Id＋Iw | > Icdqd；
    Also meet：Icd＝| Id＋Iw | > K1*Izd = K1* | Id一Iw |／2
     if only consider the value，
    Then the above inequation will be ：Icd＝| Id - Iw | > Icdqd；
     Icd＝| Id - Iw | > K1*Izd = K1* | Id + Iw |／2
    first way：if  Id > Iw ；
          then will meet with ：Id > Iw +Ｉcdqd；Id > Iw*（2+ K1）/（2- K1） the ratio differential will work
    second way：if  Id < Iw ；
         then meet with：Iw > Id +Ｉcdqd；Iw > Id*（2+ K1）/（2- K1） the ratio differential will work
③  CT break line      
P To avoid the wrong action when the CT break line,the 998 generator differential protection relay set up the function of the CT time delay line-break alarm and the CT instantaneous trip blocking protection,
1) CT time delay line-break alarm:any one of the discrepancy current is greater than 0.15Ie and the time is exceed the 10 seconds,the CT line-break alarm,but not block the differential function,which also contain the function of the self-checking of the alternating current sampling of the protection device.
    2)  CT line-break alarm：process in the fault measurement routine ,when it meets with any one of the following condition .the CT line-break can not work.
       Before starting ,the maximum current of any one side is less than 0.2Ie.  
   After starting,the maximum current ia greater than1.2Ie.
    3) it is regarded as the CT line -break when any one side current meets with the following condition.
      If there is only one zero current,then the other current is equal with the current before starting. 
notes：Electricity protection exports are 3J（C7、C8）、4J（C9、C10）、5J（C11、C12）；
       Non electricity protection exports are 6J（C13、C14）、7J（C15、C16）、8J（C17、C18）；